In a recent study, we identified a small group of unique older adults (N = 17, aged 60-80 yrs.) who are statistically indistinguishable from young adults (18-32 yrs.) in both brain anatomy and memory function. These ?superagers? offer the opportunity to investigate the biobehavioral mechanisms that contribute to successful aging, because the brain regions that distinguish them from typical older adults, and that predict memory performance, are consistently associated with not only memory performance but also motivated performance and affect, are engaged in a variety of tasks, including directing attention toward information that leads to the encoding of memories in both social and non-social contexts and also regulate control of the autonomic nervous system and the neuroendocrine system. To better understand the biobehavioral contributions to successful aging, we introduce the arousal as challenge vs. threat (ACT) model which posits that affective arousal can be either helpful or harmful to memory, depending on how it fuels motivation, which in turn is linked to the structural and functional integrity of brain networks critical for normal cognitive function. In an effort to better understand the biobehavioral contributions to successful aging, as well as their consequences for social functioning in older age, we propose a new study with targeted recruitment to enroll a large sample of superagers and study them in a multimodal way compared to typical older adults and young adults, guided by four specific aims. We treat memory as a motivated performance task and propose that superagers experience arousal as a challenge during effortful memory, whereas typical older adults experience arousal as threat (Aim 1).We will use autonomic psychophysiological methods to assess the extent to physiological patterns of challenge vs. threat mediate these relationships between experience, effort and memory performance (Aim 2). Using high-resolution structural and functional MRI we will investigate whether superagers, whose motivated performance may be characterized by more challenge, also show a more efficient neural profile relative to typical older adults whose performance may be better characterized by threat (Aim 3). Finally, we will examine the consequences of these relationships for social network size and social motivation (Aim 4). This research, if successful, will provide much needed insight into the biological mechanisms by which affect and motivation support successful cognitive aging, including the potential implications for one source of resilience, social functioning. If our research is successful, then we have potential biomarkers, integrated across the central and peripheral nervous systems, that will offer new opportunities for rational, mechanism-based strategies to promote successful aging.